There are many earlier examples of self closing gates. In general they use the weight of the barrier and an inclined plane or cam surface interacting with another cam surface or a roller, to force an extended wing member toward a null position. The extended wing member may be a farm gate, a toilet stall door, a kitchen door, or, as here, a one way gate in a store. The profile of the cam surface varies, but the principal remains the same in all cases.
Farm gates are shown, for example, in U.S. Pat. Nos. 381,063 to Ford, 785,550 to Hess & Matthews, and 1,424,913 to Kahler. Ford shows a kind of two-winged butterfly gate that turns continually in one direction. It moves between closed and open positions by means of two long levers which lift the lugs of a connecting bar up over successive detents to permit sliding motion down a subsequent inclined plane. Hess & Matthews show a typical inclined plane arrangement controlled from a distance by means of wires and pulleys. Kahler shows a sprung gate, again controlled by wires and pulleys. The quite complicated mechanism shown has internal cam surfaces and sliding bars and slots to choose between motion to an open position or to a closed position.
Typical washroom door structures are described in U.S. Pat. Nos. 4,124,955 to Kochis, 4,881,353 to Braendel et al., and 5,025,531 to McCarty. All of these are variations on the inclined plane closure whereby pushing a door causes it to lift upward, and gravity pulls the door back to a closed position.
A more interesting door closure mechanism is shown in U.S. Pat. No. 4,406,034 to Lindemann, in which a swinging kitchen door is provided with not only a roller which is pushed up an inclined track as a door is opened, and which rolls backward along that track under the force of gravity on the door, but also with a return spring that is compressed as the door opens to either side, and whose release assists gravity in forcing the swinging door back to its null, or closed, position.
All of these earlier devices have disadvantages when considered for use in one-way gates. First, of course, several of them are swing gates, rather than one-way closures. One-way closures have nonetheless been known generally for many years. Several of the earlier devices, particularly the farm gates, show un-necessary cable and pulley systems for operation from a distance, for example to permit the gate to be opened without dismounting from a car or truck. Several show undesirable exposed mechanisms which would be a safety hazard, particularly in the context of children's fingers, and therefore unsuitable in a store. In many cases gravity alone would not be satisfactory to ensure sufficiently rapid, yet gentle, closing of a gate, particularly as the weight of the gate, and hence its eccentric moment load, increases. There is a dearth of damping devices amongst the earlier gates.
It would be possible to build a functioning gate incorporating two stops into a single cam surface ramp, having integral stops at both upper and lower ends, the stops forming part of the stationary structure of the gate. Such a device would rely upon a roller mounted on a shaft, or an analogous part, to contact the upper and lower stops, and thereby limiting the range of motion of the gate. In that case, however, the shaft of the roller would carry the torque imposed in reverse motion of the gate. This is undesirable since it may result in a very large load being imposed in bending upon the relatively small diameter of a stub shaft, and worse still, at a point of stress concentration due to the geometry of a threaded hole with which the stub shaft mates, and due to the stress concentrations associated with cold formed threaded parts generally. A shaft could easily fail in such circumstances.
There is thus a need for a compact, self-closing gate with hidden mechanism to prevent, for example, finger pinching, a damping means to reduce erratic oscillation of the gate, and an augmented closing force to improve the response of the gate, all provided within a sturdy structure suited to resist opening in the opposite direction to that desired.